Scripting: silence all nested audio metastrips
This selects all sound strips in meta strips and mutes them 

import bpy
context = bpy.context
scene = context.scene
se = scene.sequence_editor
sounds_in_meta_strips = [s for ms in se.sequences_all if ms.type == 'META'
               for s in ms.sequences if s.type == 'SOUND']

for s in sounds_in_meta_strips:
    # mute the sound
    s.mute = True


Extended to append a toggle button to the Sequencer Header.



import bpy
from bpy.props import BoolProperty

def mute(self, context):
    se = self.sequence_editor
    sounds_in_meta_strips = [s for ms in se.sequences_all if ms.type == 'META'
               for s in ms.sequences if s.type == 'SOUND']

    for s in sounds_in_meta_strips:
        # mute the sound
        s.mute = self.mute_meta_strips

def draw_button(self, context):
    scene = context.scene
    layout = self.layout
    layout.prop(scene, "mute_meta_strips", toggle=True)

bpy.types.Scene.mute_meta_strips = BoolProperty(name="Mute Sounds in Metas", default=False, update=mute)
bpy.types.SEQUENCER_HT_header.append(draw_button)